meet only once; a once-met acquaintance ❍ 他的记忆力很好，我虽和他有～，但二十年后他仍记得我的名字。He has a long memory. Although I met him only once,he still remembered my name twenty years later.
半面之交bàn miàn zhī jiāo
指只见过一次面的人。only a chance acquaintance of somebody, a once-met acquaintance